Marijuana is one of the most widely used drugs of abuse, and is increasingly being ascribed therapeutic properties. Unfortunately, high-resolution structural knowledge about the marijuana receptor, called CB1, is limited. Such knowledge would aid in the development of compounds to better treat addiction, chronic pain and glaucoma. A major obstacle for obtaining CB1 structural information is the fact that CB1 is a membrane protein and thus difficult to obtain in quantities sufficient for traditional structural methods. Furthermore, like most other members of the G-protein coupled receptor family, CB1 is refractory to traditional purification procedures. In Aim I of this CEBRA proposal, we will establish conditions for expressing, solubilizing and purifying large amounts of CB1 to set the stage for crystallization studies. On a parallel track, in Aim II we will express, purify and crystallize two separate CB1 domains, the long CB1 N-terminus, and the transmembrane ligand-binding domain of a truncated form of CBI. Finally, in Aim III we will assess the function, structure and dynamics of extracellular loop E-2 in CBI. The goal of these experiments is to test the emerging hypothesis that this loop plays a universally important role in ligand binding kinetics and receptor stability in GPCRs.